Studies have been conducted to evaluate: 1. the biologic properties of oligomeric supercoiled forms of SV40 DNA; 2. the presence of oligomeric linear forms of SV40 and polyoma virus DNAs; 3. the relationship between polyoma, SV40 and BKV T antigens; and 4. whether BKV DNA sequences are present in normal and malignant human tissue. Experiments are also in progress to evaluate whether the presence of polyoma DNA, present as a recombinant DNA molecule in E. coli, is a potential biohazard to newborn mice and hamsters. BIBLIOGRAPHIC REFERENCES: Davoli, D., Ganem, D., Nussbaum, A.L., Fareed, G.C., Howley, P.M., Khoury, K.G., and Martin, M.A.: Genome structures of reiteration mutants of simian virus 40. Virology 77 110-124, 1977. Howley, P.M. and Martin, M.A.: Uniform representation of the human papovavirus BK genome in transformed hamster cells. J. Virol. 23: 205-208, 1977.